1. Technical Field
The present invention relates generally to an improved data processing system and in particular, to a method and apparatus for processing data. Still more particularly, the present invention provides a method and apparatus for traversing frames in a stack.
2. Description of Related Art
Java is an object oriented programming language and environment focusing on defining data as objects and the methods that may be applied to those objects. xe2x80x9cJavaxe2x80x9d is a trademark of Sun Microsystems, Inc. Java supports only a single inheritance, meaning that each class can inherit from only one other class at any given time. Java also allows for the creation of totally abstract classes known as interfaces, which allow the defining of methods that may be shared with several classes without regard for how other classes are handling the methods. Java provides a mechanism to distribute software to different computing platforms.
Java is able to support applications for many types of data processing systems, which may contain a variety of central processing units and operating system architectures. The Java Virtual Machine (JVM) is a virtual computer component that resides only in memory. The JVM allows Java programs to be executed on different platforms as opposed to only the one platform for which the code was compiled. Java programs are compiled for the JVM. In this manner Java is able to support applications for many types of data processing systems, which may contain a variety of central processing units and operating systems architectures. To enable a Java application to execute on different types of data processing systems, a compiler typically generates an architecture-neutral file format. The compiled code is executable on many processors, given the presence of the Java runtime system. The Java compiler generates bytecode instructions that are non-specific to particular computer architectures. A bytecode is a machine independent code generated by the Java compiler and executed by a Java interpreter. A Java interpreter is a module in the JVM that alternatively decodes and executes a bytecode or bytecodes. These bytecode instructions are designed to be easy to interpret on any machine and easily translated on the fly into native machine code.
A development environment, such as the Java Development Kit (JDK) available from Sun Microsystems, Inc., may be used to build Java bytecode from Java language source code and libraries. This Java bytecode may be stored as a Java application or applet on a Web Server, where it can be downloaded over a network to a user""s machine and executed on a local JVM. When extra speed in executing a Java program is needed, a Just In Time (JIT) compiler may be used to translate bytecodes for a method or class into native machine instructions before executing them. This can occur as late as when a method is first executed.
JVMs are required to have a backtrace facility. This facility is used in application debugging as an exception to show a backtrace of routines. Further this backtrace facility also is used for certain security aspects in which the caller of a routine needs to be identified or a stack depth needs to be determined. Currently, maintaining sufficient information to allow creation of a back trace requires building a stack frame on every entry to a method. This step may take time and affect performance.
Therefore, it would be advantageous to have an improved method and apparatus for traversing frames in a stack.
The present invention provides a method and apparatus in a data processing system for traversing a plurality of frames for a stack stored sequentially in a memory. A method block associated with a current frame is found. The method block is read to identify an offset to previous frame information in the current frame. A previous frame is located within the plurality of frames using the previous frame information.